Open locking plate lifting clamp



1953 J. .c. RENFROE OPEN LOCKING PLATE LIFTING CLAMP Filed May 2'7, 1952Patented Oct. 6, 1953 UNITED STATES PATENT OFFICE 4 Claims. 1

My invention relates to improved steel plate lifting clamps, and moreparticularly to means for selectively locking the movable jaw of a platelifting clamp in open position.

A general object of my invention is to improve plate lifting clamps ofthe type comprising a self-actuating clamping jaw.

A more specific object of my invention is to provide simple means in aplate lifting clamp selectively positionable to lock the movable jaw inopen position automatically and alternatively positionable in aninactive position.

Locking devices to lock the clamping jaw open have been heretoforeprovided, in plate lifting clamps of the general type involved herein,but

such locking devices have ordinarily utilized springs or sliding bars,or both, and such elements are expensive and may protrude and be subjectto damage and injury to operating personnel. An important object of thisinvention, accordingly, is to provide a locking arrangement which willbe sure in action, easily operated, simple and of inexpensiveconstruction.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and method of operationtogether with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawing, in which Fig. 1 is a side view of a clampin accord with my invention; Fig. 2 is an end view and Fig. 3 a bottomview of the clamp of Fig. 1; and Fig. 4 is a sectional view of the clampas seen in Fig. 1 with'a side wall removed to disclose the internalmechanism.

Corresponding elements of the clamp are identified with like numbers ineach figure of the drawing.

As seen in Figs. 1, 2 and 3, the clamp comprises a pair of parallelspaced side walls I and 2 having a vertical slot 3 formed at the bottomedges in position to receive a plate, such as plate 4, to be clamped andlifted. Body rivets 5 and 6 serve to hold the side walls in parallelspaced position, and a web I is welded in place between the side wallsto assist in this respect. In operation, a plate 4 is gripped betweenthe plateengaging teeth of pivotally mounted jaw member 8 and the ridgedsurface of a stationary jaw member 9 carried by web 1.

A crowned roller I0 is supported between the side walls by a shaft II,in a position behind web 1 and stationary jaw member 9. and the surfaceof this roller protrudes from the wall edges, as clearly seen in Fig. 1.Rollers l2 and I3 are provided outside of walls I and 2, being carriedby shaft l4, and the surfaces of these rollers extend into the slot 3 toprevent contact between a plate 4 and the edge of the side wallsadjacent the plate-receiving slot 3.

Jaw member 8 is pivotally supported on shaft M for actuation by a pairof links I5, 16. Pin ll connects the links to jaw member 8, and it willbe a apparent that upward motion of the links serves to pivot jaw member8 into clamping position, and that falling of the links retracts oropens the jaw member.

Clevis I8 is pivotally attached to the links by a transverse clevis pinI 9 having ends disposed in respective vertical slots 20 formed in theside walls. Crane hook receiving eye 2| is formed at the upper end ofthe clevis.

Clevis pin I9 is retained in position by external wall plates or pads 22and 22a welded to plates 1 and 2, respectively. These pads further serveto prevent the fingers of workmen from damage in slots 20 and preventthe entrance into the slots of any external objects which mightinterfere with the normal operation of the clamp. Plugs 22?) are screwedinto round apertures through pads 22 and 22a, and these apertures arealigned with slots 20 and positioned to permit the clevis pin l9, uponremoval of plugs 22b, to be driven out of the clamp for inspection orreplacement as desired. Plugs 221) preferably lie flush with the innerpad surfaces and do not interfere with the sliding of clevis pin IS inthe slots, and the plugs protrude externally not more than a very smalldistance to prevent catching of the plugs on persons or externalobjects. For similar reasons it may be desirable to bevel the edges ofthe pads 22 and 2211..

In order that body member 8 may be locked in an open position, aT-shaped pawl 23 is loosely supported, by means of an oversized bore 24through the base of the pawl, on a shaft 25 which extends between thewalls. An indentation 2B in the wall edges below shaft 25 permits thehead portion of the pawl to swing by gravity inwardly, toward avertically downward position, against the links l5 and 16 withoutinterference from the walls, and a notch 21 above shaft 25 provides atrap in which the head of the pawl may be engaged by manuallypositioning the head portion therein. An upwardly extending protuberanceis formed at the entrance to notch 21 over which the pawl arms must belifted, to trap the pawl or to remove the pawl from the trap.

The head portion of the pawl comprises an edge 28 adapted to engage innotches in links l5 and I6 defined by shoulders 29. The head furthercomprises surfaces 30 and 3|, formed under the arms of the T andengageable in the trapping notch 21.

Operation of the clamp is best understood by a comparison of Figs. 1 and4. The clamp is shown in Fig. 4 in open lock condition, the weight of;the clamp being supported: by plate 4. The weight of clevis l8 and ofthe links has caused the jaw member 8 to open as shown in Fig. 4, andthe plate 4 is loosely engaged in slot 3. As further seen in Fig. 4, thehead of pawl 23 has fallen into notches 26, in which position the endsurface 28 of the pawl willengageshouk ders 29 of the links upon aslight, upward motion of the links. Accordingly, if clevis [8' is liftedby a crane hook, the jaw member 8 carrnot close against plate 4 becausethe engagement of, surface 28 with shoulder. 29. prevents substantialupward motion of. link 16.. The, position of pawl 23 indicated by fullline in. Fig. 4-, accordingly, represents an open lock condition. of theclamp.

If it were desired to have the clamp grip plate l as clevis E3 wasraised, pawl 23 would be manually rotated about shaft 25' into theupward position indicated by broken lines in Fig. 4. In this upwardposition, the arms, of the pawl have been raised over the slight upwardprotuberance at the entrance to trap 2'5. It is possible to raise thepawl member to cause its head to enter the trap over the entranceprotuberance because of its loose support on shaft 25. It will beobvious that the'head of pawl 23 will remain in trap 21 until the pawlis manually lifted sufficiently for the arms to clear the entrance tothe:

trap. If the pawl is removed from the trap at a time when. jaw 8 is inclosed or gripping position, the pawl, will fall against the edges oflinks and. It as shown in Fig. 1, and the. pawl. will become effectiveautomatically thereafter when. the plate being lifted is set. down andthe. lift on clevis l8lis. released. The-clamp and pawl as seen in Fig.l, accordingly, are in pre-set. automatic' locking condition, and itwill be under-' stood that, with the pawl in the pre-set automaticlocking position indicated in Fig, 1, it will, operate automaticallyinto the open lock position' of Fig. 4 as the plate being lifted is setdown; and as the weight of the clamp is transferred from the crane hookto the plate.

If it is desired that the clamp should not lock open automatically uponsetting down. of the. load, the pawl is manually positioned in inactive;position in: the trap, as indicated by the broken lines of Fig. 4', toplace the clamp in.non-- locking condition.

While, I have, shown only certain preferred embodiments of my invention;by way of illuse tration, many modifications. will, occur. to thoseskilled in the art, and I; therefore wish to have. it understood that Iintend, in the appendedclaims, to coverall such modifications as fallwithin-the true spirit and scope of my invention.

What I'claim as new and desire to secure by Letters Patent of the UnitedStates is? 1. In a plate lifting clamp comprising a pair of spacedparallel side walls slotted at the bot-- tom to receive a plate, meansconnecting said walls to each other, a gripping jaw member pivoted tosaid walls and engageable with a plate in said slot, a lifting clevis,said walls'having aligned'slots and said clevis being movable in saidslots, a link connected between said clevis and an off-center portion ofsaid jaw member to pivotally close said jaw member upon lifting of saidclevis and link and to pivotally open said jaw member upon lowering ofsaid clevis and link, said link having an upwardly open notch, a looselymounted pawl pivotally mounted on said clamp normally hanging freelyagainst said link, said notch being positioned and proportioned toreceive said freely hanging pawl member upon opening of said jaw member,said walls having a notched trap for said pawl member for locking saidjaw member in open position remote from said link, said pawl memberbeing selectively manually rotated from its lower link engaging positionto its. upper position for engagement in said trap and removabletherefrom to hang against said link in said lower position.

2. In a plate lifting clamp comprising a pivotal jaw member and anupwardly and downwardly movable actuating link for closing and openingsaid jaw; an automatic locking pawl, side walls, means for pivotallysupporting said pawl from said walls, said walls havinga trap for saidpawl, said side walls having aligned upper slotsand a clevis slidable insaid slots, means connecting said clevis to said link, means connectingsaid wallsv to each other in spaced relationship, said trap beinggenerally above said means to retain said pawl out of engagement withsaid link, said pawl. being manually positionable in said trap toinactivate said pawl and selectively manually removable therefrominto-active automatic looking condition, and a shoulder on said linkpositioned so as to be automatically engaged by said pawl in said activecondition upon opening of said jaw member to lock said jaw memberagainst closing, saidlwalls having aligned lower slots openingdownwardly, said jaw being mountedv in. said walls, for movement. withplate gripping positionin. said lower slots.

3. In a plate lifting clamp, a pair of parallel spaced side walls,slottedto receive a plate to be. lifted, means connecting said Wallstoeach other,

a. stationary jaw and a pivotally mounted jaw in said slot, to, gripsaid plate, a movable clevis, said walls having aligned slots and saidclevis-be.- ingmovable in saidslots, a pair of parallel links connectingbetween said clevis and pivota1 jaw, said links being arranged toactuate said pivotal jaw in accord-with motion. of. said clevis andlinks,

open, locking means comprising a normallyfreely- 4.v In a plate liftingclamp, in combination, a.- pair ofspaced parallel side walls,meansconnecteing saidwalls to eacho-ther, a pivotal plate-clamp ing jawmember mounted between said walls, a

clevishaving a lower portion between said walls,

aclevis pin extending laterally through said lower: portion, said sidewalls having substantially vertical slots receiving respective ends ofsaid pin, a-

pair of links pivotally connected to said pin at respective sides ofsaid clevis and inside said walls, said links being pivotally connectedto an off-center portion of said jaw member to operate' said jaw memberinresponse to movement of said pin in said apertures, a shoulder on eachsaid link, a pawl mounted for free swinging motion on said walls andengageable with said shoulders to lock said jaw member in open position,and disabling means on said clamp for holding said pawl out of contactwith said shoulders comprising a trap into which said pawl may bemanually moved and selectively from which said pawl is manually removed,said trap being located above said link shoulders whereby to hold theshoulder engaging portion of said pawl above said shoulders when ininoperative position being effective to retain said pawl in positionaway from 6 said shoulders, said walls having aligned lower slotsopening downwardly, said jaw being mounted in said walls for movementwith plate gripping position in said lower slots.

JOSEPH C. RENFROE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 10 2,360,365 Renfroe Oct. 17, 1944 2,360,601 Waldrup Oct. 1'7,1944 2,360,602 Waldrup Oct. 17, 1944

